Contactors are commonly used in many battery operated vehicles. Contactors are used to disconnect a system load from a battery. Main contactors used in high amperage battery-powered applications (e.g., 40 A to 800 A for 24-80V battery voltages) conventionally utilize electromechanical switch components due to a combination of considerations, including cost. In particular, electromechanical configurations lend themselves to handling high currents with reasonable component costs. An electromechanical contactor can either be sealed or unsealed, although sealed versions typically cost more.
Main contactors are used in nearly all off highway electric vehicles that run on batteries. They are used primarily as a safety device to disconnect the motor controller(s) in the event of a fault and to prevent arcing when the battery is disconnected and reconnected (e.g. in forklifts during battery changes).
Main contactors can be a source of failures in these vehicles due to contact corrosion, freezing, and vibration. This is particularly true for low cost vehicles that use low quality, unsealed electromechanical contactors. So from a cost and to some degree reliability perspective it would be good to be able to eliminate the main contactor. It also requires extra space in the vehicle and an additional cable.
There exist sealed electromechanical contactors that do not have a problem with contact corrosion or freezing, but these cost more. Solid state contactors that do not have any of the previously mentioned problems also exist, but there are no commercially available solid state contactors designed to handle high currents at a reasonable cost in comparison with electromechanical contactors. In particular, in the prior art the cost of high current solid state contactors is prohibitive. As an illustrative example, in a 400 A application an unsealed electromechanical contactor may cost $20, a sealed electromechanical contactor $30-40, and conventional solid state contactors would cost $100. There are a number of reasons for the high cost of conventional solid state contactors, including the need for a large number of power FETs to provide protection from high currents in both directions in the event of an electrical fault.
For the reasons described above, it would be advantageous if a main electromechanical contactor could be replaced by a solid state solution in a battery power vehicle at a competitive cost point.